Re: [libvirt PATCH 2/2] hostdev: mdev: Lookup mdevs by sysfs path rather than mdev struct

The lookup didn't do anything apart from comparing the sysfs paths anyway since that's what makes each mdev unique. The most ridiculous usage of the old logic was in virHostdevReAttachMediatedDevices where in order to drop an mdev hostdev from the list of active devices we first had to create a new mdev and use it in the lookup call. Why couldn't we have used the hostdev directly? Because the hostdev and mdev structures are incompatible. The way mdevs are currently removed is via a write to a specific sysfs attribute. If you do it while the machine which has the mdev assigned is running, the write call may block (this should return a write error instead and it is likely a bug in the vendor driver) until the device is no longer bound to vfio which is when the QEMU process exits. The interesting part here comes afterwards when we're cleaning up and call virHostdevReAttachMediatedDevices. The domain doesn't exist anymore, so the list of active hostdevs needs to be updated and the respective hostdevs removed from the list, but remember we had to create an mdev object in the memory in order to find it in the list first which will fail because the write to sysfs had already removed the mdev instance from the host system. And so the next time you try to start the same domain you'll get: "Requested operation is not valid: mediated device <path> is in use by driver QEMU, domain <name>"

Signed-off-by: Erik Skultety <eskultet(a)redhat.com&gt; --- src/hypervisor/virhostdev.c | 10 ++++------ src/util/virmdev.c | 16 ++++++++-------- src/util/virmdev.h | 4 ++-- 3 files changed, 14 insertions(+), 16 deletions(-) diff --git a/src/hypervisor/virhostdev.c b/src/hypervisor/virhostdev.c index aa3fc8738f..ea04382d0d 100644 --- a/src/hypervisor/virhostdev.c +++ b/src/hypervisor/virhostdev.c @@ -1975,7 +1975,7 @@ virHostdevReAttachMediatedDevices(virHostdevManagerPtr mgr, virObjectLock(mgr->activeMediatedHostdevs); for (i = 0; i < nhostdevs; i++) { - g_autoptr(virMediatedDevice) mdev = NULL; + g_autofree char * sysfspath = NULL;

virMediatedDevicePtr tmp; virDomainHostdevSubsysMediatedDevPtr mdevsrc; virDomainHostdevDefPtr hostdev = hostdevs[i];